1. Technical Field
The present invention relates to improvements in telescopic gun sights and, more particularly, to an improved windage correction system for a telescopic gun sight which includes a generally horizontal windage correction scale operative to provide instant windage correction target alignment and including instant windage correction target alignment values positioned at point-specific spaced-apart locations on the generally horizontal scale with specific instant windage correction target alignment values corresponding to selected distance amounts calculated for a selected bullet type and weight.
2. Description of the Prior Art
Present telescopic sites used on rifles and other firearms, generally comprise a cross-hair reticule positioned within the scope for referencing the hunter's vision with respect to a target. A hunter “sights in” or “zeros” the scope by firing bullets in a trial-by-error method and repetitively adjusts the reticule in the scope until the center of the cross-hair of the reticule aligns with the impact position of the bullet on the target. Such a method of zeroing a rifle requires considerable time and the costly firing of bullets.
U.S. Pat. No. 2,094,623 issued to F. E. Stokey in 1937, discloses a telescopic sight in which two reticules are utilized to enable the rifle to be zeroed in with a single shot. The Stokey device, however, was quite expensive and complicated. Also, because the hunter always views two reticules within his field of vision through the scope, it was quite possible that the hunter would inadvertently sight on the incorrect reticle. Also, the reticule which was sited in on target, could be off center from the field of vision through the scope causing further confusion and irritation to the hunter. Further, the hunter was shooting upside down with the Stokey scope, because the image through the scope was inverted due to the use of an objective and an ocular lens.
While the Stokey scope of 1937 suggested one-shot sighting, the inherent disadvantages, expense and complication of the system voided its general use. Since 1937, the prior art has suggested the use of an inverting tube to erect the object to be viewed through the scope by the hunter thus, eliminating upside down shooting by the hunter. The use of an inverting tube further establishes the center of the cross-hair wires at the center of the scope's field of vision despite adjustment of the cross-hair reticule relative to the image being viewed. The advent of the inverting tube was thus well received by the hunter.
When using an inverting tube within a scope, the reticule is positioned at the eye piece end of the tube. This is because the positioning of the reticule at the object end of the inverting tube causes the magnification of the cross-hairs of the reticule at high powers of the scope, particularly where the scope has zoom capabilities for changing the object's magnification. Such magnification of the cross-hair wires is annoying to the hunter, blocking portions of his view. Thus, present day scope manufacturers utilize an inverting tube with cross hair wires positioned at the eye piece end of the inverting tube.
Besides the problem of multiple firings to sight-in present day scopes, a problem of parallax exists when using the scope to shoot at close range. Parallax is caused by the cross-hair wires lying outside the image plane in conjunction with the hunter varying the position of his eye relative to the scope as he does not each time look across the cross-hairs at the same visual angle.
Further problems with such conventional scopes include the addition of devices which serve to approximate range and determine the “hold over” or aiming point in view of the range of the target. Particularly, the rifleman must judge the distance of the object and then compensate for the drop of the bullet in view of the weight and velocity of the bullet. Thus, the hunter must point the scope above the target in order for the bullet to drop onto the target. All of these range finding devices, however, add clutter to the hunter's field of vision and are particularly annoying when the hunter is shooting at close range and thus not using the range finding devices.
Such range finding devices include, for example, the use of a transparent reticule disc at one end of an inverter tube, which bears separate circles for denoting range and drop of the bullet, see for example U.S. Pat. No. 3,392,450 issued to G. L. Herter et al. on Jul. 16, 1968 or Shepherd, U.S. Pat. No. 4,403,421, issued on Sep. 13, 1983. Other such range defining devices include stadia lines which take the form of two parallely disposed horizontal lines positioned across the field of view of the hunter for his use to determine whether the object fits within the lines in order to gauge distance of a targeted object. However, despite the various types of range finding indicia used with scopes of the prior art, there has been precious little development or improvement in the methods and devices available to hunters and shooters to correct for wind, and as wind correction is at least as critical to a successful shot as finding the range to the target, there is a need for significant improvement in this area.
There are several simple formulas available to calculate the deflection due to a crosswind. One which is used in the art is as follows: z=w*(t−X/v0) where z is the deflection, w is the wind speed, t is the flight time of the bullet to the target, x is the distance to target and v0 is the muzzle velocity. This formula is most commonly used with metric units, with velocities in meters per second, time in seconds and distances in meters. The only unknown parameter in the above formula is the bullet flight time (which generally may be found in manufacturers' tables).
Another widely used formula is the United States Marine Corps formula, which is used as follows: After determining wind direction and speed, the following formula is applied: Range in 100 Yds.×Speed in MPH/15 (math constant)=MOA Windage. For instance, if your target is 300 yards away, and there's a 10 MPH wind, you would plug the numbers into the formula like this: 3×10=30/15=2 MOA. Click-in the two minutes of angle into the scope in the direction of the wind and aim dead-on. It should be noted, however, that one additional concern with the Marine formula is that it is only accurate at 500 yards or less. With a target that is farther away, the mathematical constant must change, as shown here: 600 Yards: Divide by 14, 700 Yards: Divide by 13, 800 Yards: Divide by 13, 900 Yards: Divide by 12 and 1,000 Yards: Divide by 11.
To perform all these calculations immediately prior to taking the shot is a difficult task to say the least, and therefore there is a need to improve and streamline the task of determining appropriate windage corrections. It is, therefore, an object of the present invention to provide an improved telescopic sight which adds the advantages of the prior art without their attending disadvantages.
It is yet another object of the invention to provide a telescopic sight which includes an easily used windage correction system and method by which windage corrections for shots may be quickly and accurately determined.
It is yet another object of the present invention to provide a telescopic sight for use with a firearm which includes a secondary reticule having a windage correction scale imprinted thereon which is removed from the field of view in the scope when the magnification of the scope approaches its maximum magnification setting.
It is yet another object of the present invention to provide a telescopic sight having a generally horizontal windage correction scale imprinted on either the primary or secondary reticule, the scale operative to provide instant windage correction target alignment and including instant windage correction target alignment values positioned at point-specific spaced-apart locations on the generally horizontal scale with specific instant windage correction target alignment values corresponding to selected distance amounts calculated for a selected bullet type and weight.
It is yet another object of the present invention to provide a telescopic gun sight with a windage correction scale which requires only minimal computation prior to use, and will not substantially slow or retard the aiming and shooting process.
Finally, an object of the present invention is to provide an improved telescopic sight having a windage correction scale which is relatively simple and durable in construction and is safe, efficient and effective in use.